Project Summary The ability to mount an effective immune response is critical for human health. Toll-like receptors (TLRs) are transmembrane proteins expressed on phagocytes and other cells that act as sensors of microbial infection. Recent studies have underscored the importance of TLRs in innate and adaptive immunity as mice deficient in TLR signaling have defects in controlling bacterial and viral infections. Despite the indentification of several genes required for TLR signaling, a clear picture of how TLR signaling complexes are assembled and how assembly is regulated is lacking. This proposal will investigate cellular and molecular aspects of TLR signal transduction. We will focus on the characterization of the four essential TLR adaptor proteins in terms of their localization and recruitment to membranes bearing activated TLRs. Cis-acting domains that mediate adaptor localization and recruitment to TLRs will be identified and mutated as a means of addressing the functional significance of adaptor localization in TLR signaling. Trans-acting factors that regulate adaptor localization will be identified with a particular focus on the transport regulation by phosphoinositides. The successful completion of this project will yeild important insight into cellular control of TLR signal transduction and thus, mechanisms of immunity.